Hot-air furnaces or hot-air heaters as above can be classified broadly into the following three types:
(1) a furnace, drum unified type; PA1 (2) a furnace, combustion chamber and smoke tube type; PA1 (3) a furnace, combustion chamber and heat exchanger type.
These three types are shown in FIGS. 12(a) to (f) of the accompanying drawings.
The furnace, drum unified type is shown in FIG. 12(a), in which 41 denotes a drum, 42 a burner, a 43 a flame, 44 a fan, 45 a discharge port for hot air, and 46 a thermal resisting filer. The flame 43 is generated by the burner 42 at the lower part of the drum 41, and combustion gas is heat-exchanged and loses its temperature while passing through the drum 41 and the heat resisting filler 46 at the upper part thereof, and is exhausted from an exhaust port 47. Air flow taken into the drum 41 by the fan 44, in the direction of the white arrow I, is heated while going around the drum 41, and is discharged in the direction of the white arrow II from the discharge port 45, and is then supplied to a desired place, for example, into a greenhouse, as hot air. FIGS. 12(e) and (f) are sections along the E--E and F--F in FIG. 12(a). In FIG. 12, solid line arrows show combustion gas flow and the white arrows, as mentioned above, air flow.
A furnace, combustion chamber and smoke tube type is shown in FIGS. 12(b) and (c). The same reference numerals are applied to the same parts as are shown in FIG. 12(a), and 48 denotes smoke tubes. Air taken in by the fan 44 is heat-exchanged and heated by the combustion chamber 50 and the smoke tubes 48, and is discharged from the discharge port 45. Accordingly, a hot-air furnace of this type is called a furnace, combustion chamber and smoke tube type.
Among the hot-air furnaces of the types described, the one shown in FIG. 12(a) was developed by the present applicant and was published in Japanese Patent Publication (Unexamined) No. 297631/1988. A furnace, combustion chamber and heat exchanger type is shown in FIG. 12(d), and the same reference numerals are applied to the same parts as are shown in FIG. 12(a). Further, 49 denotes a heat-exchanger and 50 the combustion chamber. Combustion gas generated in the combustion chamber 50 is exhausted form the exhaust port 47 via the heat-exchanger 49. While air taken in by the fan 44 as shown by the white arrow I is heat-exchanged and heated by the heat-exchanger 49, then heated further around the combustion chamber 50, and finally discharged in the direction of white arrow II from the discharge port 45.